Ergonomics and human functions are a fundamental part of good product design. Product usability, user-product performance, user satisfaction, and product safety and comfort are particularly important for devices that are in physical contact with the user for extended periods of time, such as, but not limited to, in-ear devices including earphones, hearing aids, and ear plugs. Comfort may be considered the most important factor regarding product compliance for products that are being worn. Ear interfacing fit and comfort for such products may be optimized through a myriad of design criteria including: tip insertion diameter, geometry, and material construction which reside internal to the External Auditory Canal (EAC), concha bowl housings geometry and their materials, as well as the geometry, weight and construction materials of behind-the-ear (BTE) type worn devices. Products not primarily worn for extensive periods of time, but used as tools for medical applications (e.g., ear-based drug delivery systems) have other factors besides comfort as a design consideration. Still other products that play music or provide a means of communication or information will also introduce further design considerations.